U.S. Pat. No. 4,594,468 teaches that it is desirable to have a low iso/normal ratio of paraffins in gas oils made from Fischer Tropsch catalysts. The examples show normal/iso ratios of from 2.7:1 to 7.5:1 (iso/normal ratios of from 0.13:1 to 0.37:1) in conventional processes and from 9.2 to 10.5:1 (iso/normal ratios of from 0.095:1 to 0.11:1) for examples of its invention.
U.S. Pat. No. 5,135,638 discloses isomerizing a waxy feed over a catalyst comprising a molecular sieve having generally oval 1-D pores having a minor axis between 4.2 .ANG. and 4.8 .ANG. and a major axis between 5.4 .ANG. and 7.0 .ANG., with at least one group VIII metal. SAPO-11, SAPO-31, SAPO-41, ZSM-22, ZSM-23 and ZSM-35 are disclosed as examples of useful catalysts.
U.S. 5,689,031 teaches a clean distillate useful as a diesel fuel, produced from Fischer-Tropsch wax. The isoparaffin/normal paraffin ratio is given as being from 0.3:1 to 3.0:1, preferably from 0.7:1 to 2.0:1.
U.S. 5,866,748 teaches a solvent (not a diesel fuel) produced by hydroisomerization of a predominantly C.sub.8 -C.sub.20 n-paraffinic feed. The isoparaffin/normal paraffin ratio is given as being from 0.5:1 to 9.0:1, preferably from 1:1 to 4:1.
Two papers, "Studies on Wax Isomerization for Lubes and Fuels" Zeolites and Related Microporous Materials: State of the Art 1994 Studies in Surface Science and Catalysis, Vol. 84, Page 2319 (1994), and "New molecular sieve process for lube dewaxing by wax isomerization" Microporous Materials 2 (1994) 439-449, disclose dewaxing by a catalytic (Pt-SAPO-11) wax isomerization process. These papers disclose isomerization selectivity for n-hexadecane of from 93% to 84% at 89% to 96% conversion, respectively, for iso/normal ratios of from 7.4:1 to 20.7:1. A third paper, "Wax Isomerization for Improved Lube Oil Quality," Proceedings, First International Conference of Refinery Processing, AlChE Natl. Mtg, New Orleans, 1998 discloses isomerization selectivity for n-C.sub.24 lube oil of from 94% to 80% at 95% to 99.5% conversion, respectively, for iso/normal ratios of from 17.8:1 to 159:1.